Certain advantages exist for an internal combustion engine that uses a storable liquid oxidant in place of the ambient atmosphere as a source of oxygen to combust the fuel. In such a case, two storage tanks are required, one for the fuel and one for the oxidant. The two storage tank requirement may be inconvenient in certain applications, submarine service, for example. The present invention includes methods and apparatus wherein the liquid oxidant is formed locally from air, water, exhaust and energy.